When producing a ceramic structural body with a large diameter, a method of first forming a number of ceramic structural bodies with small diameters and bonding them to form a ceramic structural body with a large diameter may be more preferable than directly producing a ceramic structural body with a large diameter. A honeycomb structural body made of ceramics used as a filter for particulate matter or as a catalyst carrier for an exhaust gas purification apparatus, for example, may be exposed to an extreme temperature change and the like according to the environment. Depending on the temperature characteristics of the materials forming the ceramic structural body, fabricating a structural body with a large diameter by bonding a number of structural bodies with small diameters may be more preferable than directly producing a structural body with a large diameter. In the case of a catalyst carrier for an exhaust gas purification apparatus, a wall in the structural body is made thinner in order to reduce the pressure loss, increase the effective catalytic area and the like. For manufacturing a ceramic structural body with such a thin wall, fabricating the structural body by bonding structural bodies with small diameters may be more preferable than directly forming the structural body with a large diameter in terms of an increase in the production yield.
Conventionally, in the process for producing a ceramic structural body with a large diameter by bonding a number of ceramic structural bodies with small diameters, the bonding work has been carried out by hand. Such manual work comprises, for example, bonding a ceramic structural body A with a ceramic structural body B to obtain a ceramic structural body C, bonding the ceramic structural body C with a next ceramic structural body D to obtain a ceramic structural body E, bonding the ceramic structural body E with a next ceramic structural body F to obtain a ceramic structural body G, and so forth. However, this method has the following problems.
(1) Increase in Working Efficiency is Limited.
When fabricating a ceramic structural body with a very large diameter, the number of ceramic structural bodies with small diameters to be bonded may unduly increase, resulting in an increase in the amount of work involved. Since the number of bonding operations required is equivalent to [(the number of required structural bodies with small diameters)—1], a great deal of manpower is required for obtaining one large diameter ceramic structural body, which increases the cost.
(2) Increase in product quality is limited.
When bonding two or more ceramic structural bodies, a bonding agent is applied to the surfaces of the ceramic structural bodies to be bonded and two ceramic structural bodies are pressed from the outside. In this instance, even if the bonding agent is uniformly applied to the surfaces to be bonded, the pressure may not be uniformly transmitted, giving rise to an uneven distance between bonded surfaces. Specifically, it is difficult to bond two ceramic structural bodies having completely parallel bonded surfaces. If a ceramic structural body is dried under such bonding conditions, cracks tends to occur between the bonded surfaces, resulting in low strength of the fabricated ceramic structural body.
When fabricating a ceramic structural body with a large diameter by bonding a number of ceramic structural bodies with small diameters, the ceramic structural bodies with small diameters having the same configuration and dimensions are used in many cases. It is difficult to accurately position the bonding surfaces of these ceramic structural bodies, even if these are placed on a flat plane. As a result, a fabricated ceramic structural body may have positional gaps in the vertical and horizontal directions. Such a ceramic structural body is undesirable, because it has a low open frontal area, which gives a low effective filter area and a great pressure loss. As a result, the filter performance is adversely affected.